In this investigation, conscious squirrel monkeys, free-moving within individual cages, are subjected to chronic, intermittent hypothalamic stimulation for periods ranging from 1 to 24 months. Stimulation is performed through indwelling electrodes connected to implanted preprogrammed, battery-powered electronic microstimulators developed in this laboratory. Control animals are treated identically except that their stimulators are nonfunctional. Half of all animals are on basal monkey chow diets. The diets of the other half are supplemented with varying amounts of cholesterol and animal fat. Periodic measurements are made of weight gain, blood pressure, plasma lipid and lipoprotein concentratons and serum 'clinical' chemistry levels. At sacrifice, morphologic observations at the gross, light and electron microscopic levels are made on aortas and coronary arteries. Correlations are sought of the degree and severity of morphologic changes with region of hypothalamus stimulated, duration, frequency and intensity of stimulation, blood pressure changes and plasma lipid and lipoprotein concentrations. It is expected to use the data in two ways: 1) to develop a nonhuman primate model for the investigation of neurogenic factors in early atherosclerosis and 2) to support recent clinical and epidemiologic evidence that neuropsychologic mechanisms may constitute important risk factors in atherogenesis.